Smoking cessation services are not widely available in many low-resource settings, because trained counselors are scarce, and pharmacological approaches are priced beyond the reach of many smokers. The problem is especially acute in low- and middle-income countries, where most tobacco-attributable deaths occur. The proposed study tests a set of novel, low-cost behavioral approaches for smoking cessation in large workplaces in Thailand. The main approach, drawn from behavioral economics, is a commitment contract, an agreement whereby individuals bind themselves to achieve a goal in order to maintain self-control. Specifically, a participating smoker deposits money that is returned only if the person quits successfully. The study cross-randomizes commitment contracts for smoking cessation with two elements to promote behavior change: financial and social incentives. We propose to conduct and evaluate a randomized controlled trial with a 3-month intervention and follow- ups at 3, 6, and 12 months in a sample of 3,200 smokers across 100 firms. The study will track an additional 4,800 smokers from the same firms who choose not to participate in the intervention. The proposed intervention randomly assigns participants to one of four types of commitment contract, including no contract, and to one of three levels of cash bonus for quitting, including no bonus. The contracts are structured such that some participants receive a cash bonus for quitting; others are randomly assigned to a two-person team and receive a cash bonus only if both members quit; and others have a choice between the two incentive schemes. The factorial design will permit the identification of the effect of several causal mechanisms on quitting: financial commitment, peer pressure, social support, and monetary rewards. The study will provide some of the first evidence on the value of supplementing a basic commitment contract with cash rewards and social commitment. The study further compares the cost per quitter of each type of commitment contract to standard clinical approaches for smoking cessation. In so doing, the study will inform policymakers about a set of novel, inexpensive ways to promote good health behaviors.